TM 5-6675-316-14
Font interface board III J13. Performs the operations required for pro-
per character selection from the character disc, width data and FLASH logic.
(1) Disc speed control uses the 5 mHz master clock (MASCLK) which is gated
through a divide-by-3 counter (counter 1). The output of counter 1 sets the range
of speeds available. The output of counter 1 divided by counter 2. The output
of counter 2 is controlled by counter 4. The 5B07 signal loads FLXD1 thru FLXD4
into counter 4. This enables counter 4 to change the divisor of counter 2. The
output of counter 2 is applied to counter 3. The output of counter 3 is a reference
frequency used to control-the speed of the disc (SPDREF). SPDREF is applied to Nand
gates 2 and 3. The amplified signal from the strobe track on the character disc is
and 2, then to Nand gate 1 via JK flip-flops 1 and 2. The output of Nand gate 1 is
a 200 ns pulse for every dark-to-clear transition on the disc. This output is fed
to JK flip-flop 3. JK flip-flop 3's output is fed to Nand gates 2 and 4 and
Register 1. The outputs of Nand gates 2; 3, 4 and 5 are compared with STBEDG and
the difference of the two frequencies controls the output of register 1. This
changes the disc speed until both frequencies are identical.
(2) Width select data on the strobe track on the font disc contains 112
sectors. Each sector is divided into 18 parts. The first 4 parts are opaque, the
5th clear, 6th and 7th opaque and the last 11 alternate in a black-and-white pat-
tern.
The circuit that detects three consecutive dark divisions is called MP counter 5.
MP counter 5 generates an output pulse after 1-3/4 dark divisions have been
detected. Therefore, a pulse-will be generated at the beginning of each sector.
The other opaque divisions of the sector are too short to allow MP counter 5
to ouput a pulse. Each transition and missing pulse is detected by FF1, 2 and 6
from the STBTRK signal. The output of FF2 produces a signal called SEDG+MP. This
represents every transition plus the MP. The pulses go through a divide-by-3 counter
(counter 1). Each pulse output represents one-font. These pulses are fed-to
counter 2 which keeps track of the font position. MP counter 5 is kept in a preset
condition as long as the strobe track is clear. When a dark division appears, MP
counter 5 is released. MP counter 5 is preset by the next clear position through
FF3 via counter 2. When three dark divisions are detected, counter 2 will overflow
and generate the MP. This disc is designed so that DTATRK1 is opaque for 111 posi-
tions around the disc adjacent to the MP.
DTATRK1 is clear for only one sector.
Gating MP and DTATRK1 generates an origin pulse. The origin pulse is generated when
the first character position approaches the character flash window. When this oc-
curs, counters 4 and 3 are preset to 1. Gating the MP with inverted DTATRK signal
will produce three pulses. These pulses cause counters 3 and 4 to keep track of the
disc position. The outputs of disc position counters 3 and 4 and font position
counter 2 go into comparators (COMP) 1, 2 and 3. The other inputs to the compara-
tors are font position register R3 and disc position registers R4 and R5. The reg-
isters are loaded with 1/0 instructions 5B04 and 5D04 (the disc position and font of
the character whose width is being requested). When the disc is in position to be
read, two signals, CHEQ and FEQ are generated. When signal 5D04 is present, it
sets FF4. FF5 output (WDTHALW) goes high on the next MP. The following signals are
required to allow data to be loaded into registers R1 and R2: FEQ, SEDG+MP, WDTHALW
and CLK. The output of Nand gate N4 produces properly timed and clocked signals
relative to the data-tracked signal so that data is properly loaded into the width
registers (R1 and R2). The width registers hold width data until 4704 Input In-
struction (147) width of character from the program processes the information.
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